An image display system which includes an image input device for capturing an image of manuscript or other subjects (such as a document camera) and an image display device for displaying the image captured by the image input device (such as a projector) is known. According to the image display system having this structure, a part of the subject can be expanded (enlarged) for display by using a zoom function of the image input device or the image display device (for example, see Japanese Patent Publication No. 2005-123707).
For expanding apart of the image by the zoom function, however, a user needs to perform both operation for specifying an expansion rate and operation for specifying a position to be expanded (expansion position) by press of an operation key or by other methods. Moreover, the user needs to repeatedly press the operation key in some cases for specifying the expansion rate or expansion position, which is complicated for the user.